Memory tube



A. SALECKER June 18, 1957 MEMORY TUBE 2 Shets-Shset 2 Filed Feb. 18, 195;

' FIG.5

INVENTOR.

ANTON SALEOKER MEMORY TUBE Anton Saiecker, Poughkeepsie, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application February 18, 1953, Serial No. 337,544

4 Claims. (Cl. 29-2514) This invention relates to electrostatic memory tubes of the cathode ray type wherein binary information is stored in the form of charges established on the surface of a dielectric target by potentials applied to a capacitatively coupled backing plate while the cathode beam impinges an elemental target region. In particular, this invention is directed to a method of fabrication of a target assembly comprising the dielectric target, backing plate, barrier grid and collector grid electrodes.

The principle of electrostatic storage involves setting up one of two distinguishable charge states at discrete regions on the target surface and, at a later interval, in determining which of the two charge states was established in each region. In establishing the charge states, the cathode beam is directed to an elemental target region and secondary electrons are emitted therefrom and attracted to a collector electrode placed near the target end of the tube. The potential of the bombarded region and collector electrode tend to become equalized and the charge established on the elemental region is determined by modulation of the backing plate which is capacitatively coupled with each elemental target region. For example, if the backing plate is held at a negativepotential at the time the beam is turned off, the bombarded region will become positive with respect to the collector electrode whereas if thebacking plate is not modulated or a modulating pulse terminated before the beam is turned off, the region will remain at the collector electrode potential.

During bombardment of an elemental region, some secondary electrons collect in the form of a space charge and tend to rain back on the target surface rather than flow to the collector electrode and, since some of the elemental regions adjacent the one bombarded will be positive, there is a tendency to neutralize their charges. A barrier grid electrode is placed on or near the target surface to shield one storage region from another and to reduce this effect of secondary electron redistribution. -A system employing a barrier grid storage tube of this type 'is disclosed in the copending application of D. R.

-Young and R. 'B. De L'ano, Ir., Serial Number 357,608,

filed May 26, 1953.

In previous tube structures, the barrier grid and collector grid are constructed of a prewoven wire mesh mounted on a metal frame, and particular difiiculty is encountered in providing uniform tension to the mesh wires so as to avoid shorting between these electrodes when they are subjected to high temperatures during the process of outgassing the tube.

Accordingly, it is an object of this invention to provide an improved method for assembly of the target electrode structure for a barrier grid memorytube whereby critical electrode spacing may be accurately maintained.

Another object of this invention is to provide a novel method for fabricating grid structures capable of withatent F Patented June 18, 1957 standing high temperature vacuum baking without warping or shorting to adjacent electrodes.

Still another object of this invention resides in an improved method of fabrication of grid electrode structures.

Other objects will be pointed out in the following description and claims and illustrated in the accompanying drawings which disclose, by way of example, the principle of the invention and a contemplated mode of applying the principle.

In the drawings:

Fig. 1 illustrates a storage tube of the barrier grid type wherein the target assembly is supported upon a reentrant stem.

Figs. 2 and 2a illustrate an alternative method of mounting the target assembly.

Fig. 3 is a plan view of an improved barrier grid subassembly comprising a ceramic frame, mica target and barrier grid.

Fig. 4 is a sectional view taken on the line 44 of Fig.3.

Fig. 5 illustrates the structure of a collector grid subassembly comprising a ceramic frame and collector grid.

Fig. 6 illustrates a method employed for winding the grid wires on the ceramic frames.

Fig. 7 illustrates the complete target assembly comprising the barrier grid and collector grid subassemblies mounted in a supporting member.

Referring to Fig. l, the memory tube illustrated comprises an envelope 1 of glass or other suitable material within which is positioned an electron gun for forming and focusing an electron beam upon a target 2. The beam is produced by a thermionic cathode 3 and is turned on under control of an apertured grid electrode 4. An anode electrode 5 is positioned in alignment with the cathode beam and accelerates the electrons emitted from the cathode 3. Electrodes 6 are shield electrodes formed from apertured metal discs and are spaced along the path of the cathode beam. Two pairs of deflection plates 7 direct the beam to particular elemental regions on the surface of the target 2 as determined by potentials applied thereon by conventional means for producing the desired type of target scansion. The target assembly is mounted on a reentrant stem and is supported by wires 8 as shown in Fig. 1. An alternative method of mounting the target assembly is illustrated in Fig. 2 with leads 9 which connect the electrodes comprising the target assembly, held in the tube face at equidistant points, as shown, and the assembly supported in contact with the inner surface of the envelope 1. The complete target assembly is shown in detail in Fig. 7 and, in this assembly, a barrier grid 10 is held in direct contact with the surface of target 2 and a collector grid 11 is spaced from the barrier grid a distance of approximately 0.010 inch. The spacing of the barrier grid 10 from the target 2 is not too critical, however, ithas been found that the effect of redistribution becomes greater as the spacing is increased with best results obtained with the barrier grid wires in direct contact with the target surface.

The target 2 (Figs. .3, 4 and 7) comprises asheet of dielectric material such as mica which'is approximately 0.002 inch thick and has a high resistivity product and dielectric constant. A backing plate 12 is formed on one surfaceof the mica target 2 by the evaporation of aluminum as in well known coating processes. The thickness of the mica sheet is made small compared with the spacing between the grid wires in orderto allow the backing plate to swing a large fraction of the surfacearea between grid wires with which it is capacitively coupled.

The grids and 11 are supported on rectangular frames 13 (Figs. 3, 4 and 5) formed of a ceramic material commercially known as Alsimag 475 which has a coeficient of expansion comparable to that of the tungsten grid wires. Although rectangular frame members are described hereafter, it is contemplated that circular or other shaped frames may be employed if desired. The use of this ceramic material allows the frame and'g'rid wires to expand and contract to an equal degree during the process of outgassing the tube during which'tirne the target as sembly is subjected to a temperature of approximately 350 C. in this manner, the grid wires are not subjected to stretching and remain in a substantially uniform coplanar relationship at all times. The ceramic frame 13 is first ground to provide a flat surface: 14 as shown in Fig. 4. The frame is then baked at a temperature of 850 to 900 C. and a thin coating of silver paste 15 (Dupont 4822) applied to the outer edge of surface 14, as shown in Figs. 3 and 4, followed by further baking at 700 C. for approximately one half hour. The silver paste 15 provides electrical contact between the grid wires which are wound on the ceramic frame 13 as will be described.

In fabricating the barrier grid section of the target unit, two frames 13 are placed in juxtaposition on a winding machine mandrel 16, as shown in Fig. 6, with the fiat ground surfaces 14 outward, and a mica target 2 is positioned on each frame with the side to which the aluminum backing plate 12 has been applied placed in contact with the ground surfaces 14.

The tungsten grid wire employed is approximately 0.0006 inch in diameter and is small enough and so spaced as to intercept only a fraction of the cathode beam which has a diameter of approximately 0.010 inch. The grid is cross wound with 100 turns per inch from a single strand of wire with the winding tension controlled by a drag cup motor 17. Cross winding the grid wires in two layers at right angles to one another forms a rectangular mesh as shown in Fig. 3, however, the individual strands are not interwoven. If desired, a partially interwoven mesh may be obtained by alternately winding a single turn in each direction, however, sufficient rigidity is obtained by overlapping the two cross wound layers of wires in target assemblies of conventional dimensions. It is contemplated that a plurality of frames be positioned in alignment on a many sided winding element 16 and a plurality of grid units wound in the above described manner using a single strand of grid wire.

After the grids are wound, the wires are secured to beveled edges 18 of each of the frames 13 by application of a ceramic cement 19 (commercial Sauriensen cement),

as seen in Fig. 4, and the portions of the wires joining In winding the collector grid 11 (Fig. 5), a pair of frames 13 prepared in the same manner are positioned on the mandrel 16 in back to back relationship. The grid wire is wound from a single strand with controlled tension as described in connection with. the barrier grid, however, the strands are wound at to the edge of the frame 13 and spaced at 150 turns per inch. The wires are secured to the beveled edges 18 with a ceramic cement and the joining portions severed as before to fabricate two collector grid units simultaneously. A nickel connecting strip 22 is then secured to the grid wires at one side of the ceramic frame in the same manner as with the barrier grid. The barrier grid and collector grid units are placed face to face with the grid wires spaced approximately 0.010 inch apart and droplets of ceramic cement 23 are applied to rigidly hold the frames 13 of the two units in this position as shown in Fig. 7. By placing the collector grid 11 close to the barrier grid 10, the positive field in front of the target is further increased and a greater reduction in secondary redistribution is obtained. The assembled target unit is mounted in a stainless steel supporting member 24 which is in turn supported by a plurality of supporting wires 3 held in the rcentrant stem as shown in Fig. 1. The reentrant stem is spliced to the main tube section in which the conventional gun structure is mounted and the tube is then subjected to pumping and high temperature vacuum baking (350 C.) as before mentioned without detrimental change in the critical electrode spacing.

While there have been shown and described and pointcd out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A method of fabricating a barrier grid and target assembly for a cathode ray tube comprising the steps of coating the central area of one surface of a sheet of dielectric with conductive material, coating the edges of one surface of a ceramic frame member with conductive material, said frame member having a central opening smaller than said dielectric sheet, assembling said ceramic frame member and dielectric sheet with the coated central area of said sheet within the central opening in said frame and spaced from the conductive coated edges thereof, winding a single strand of grid wire about said assembled unit to form a network of parallel spaced wire sections in contact with the other surface of said dielectric sheet and the conductive coated edges of said frame, and securing said strand sections to the edges of said ceramic frame.

2. A method of fabricating a target assembly for a cathode ray type tube comprising, coating the central area of one surface of a dielectric sheet with conductive material, applying a conductive coating to the edges of one surface of a first ceramic frame having a central opening smaller than said dielectric sheet, assembling said ceramic frame and dielectric sheet with the coated central area of the latter within the central opening in said frame, winding a single strand grid wire about said sheet and frame to form a network of parallel wire sections in contact with the uncoated surface of the dielectric sheet and the coated edges of said frame, securing said strand sections to the edges of said frame, applying a conductive coating to the edges of one surface of a second frame, winding a second grid on said second frame from a single strand of grid Wire, securing the strands of grid Wire to the edges of the second frame, joining said first and second frame so as to position said grids in fixed spaced relationship.

3. A method for fabricating a barrier grid and target assembly for a cathode ray tube comprising the steps of coating the central area of one surface of a sheet of dielectric with conductive material, assembling said dielectric sheet over the central opening of a frame memher, with the coated area within said opening and spaced therefrom, said opening being smaller than said sheet, winding a single strand of wire about said assembled unit to form a network of spaced parallel wire sections in contact with the other surface of said dielectric sheet and rigidly supporting said sheet relative to said frame, and securing said strand sections to the edges of said frame.

4. A method of fabricating a target assembly for a a single strand of grid wire, and thereafter joining said ath d my type tubg i i ti th t al first and second frames so as to position said grids in area of one surface of a dielectric sheet with conductive fi ed Spaced r l i hipmaterial, assembling said sheet and a frame member having a central opening therein with the coated cen- 5 References Clted 111 the file of thls Patent tral area of the sheet within the opening in said frame, UNITED STATES PATENTS winding a single strand of grid wire about said sheet 2,527,127 Gormley et aL Oct 24, 1950 and frame to form a network of parallel wire sections in contact with the uncoated surface of the dielectric FOREIGN PATENTS sheet, securing said strand sections to the edges of said 10 124,909 Australia July 31, 1947 frame, Winding a second grid on a second frame from 

